Process for preparing zeolite powder of type A (IV)

ABSTRACT

There are produced crystalline zeolite powders of Type A with the composition 
     
         1.0±0.2 M.sub.2/n O:Al.sub.2 O.sub.3 :1.85±0.5 SiO.sub.2.y H.sub.2 O 
    
     where M is a metal cation, n is its valence and y has a value up to 6 with 50 weight % of the particles not over 4.9μ and with a particle spectrum 
     
         ______________________________________                                    
 
    
     Fraction (μ)                                                           
              Portion (weight %)                                          
______________________________________                                    
 &lt;3           10 to 60                                                    
 &lt;5           55 to 95                                                    
&lt;10           93 to 99                                                    
&lt;15            96 to 100                                                  
______________________________________                                    
 
     by hydrothermally crystallizing a SiO 2 , Al 2  O 3 , Na 2  O and water containing alkali aluminate, water, silicate synthesis mixture with an optional tempering step wherein in a given case during the crystallization or tempering step instead of stirring shearing forces are employed. The process comprises mixing with stirring (1) an aqueous alkali silicate solution and (2) an aqueous sodium hydroxide with a NaOH content of 0.1 to 500 grams/l and/or (3) aqueous sodium aluminate liquor which contains 0.1 to 100 grams/l of Al 2  O 3  and 1 to 200 grams/l of Na 2  O, one of components (1) and (2) or (3) being present in a container and the other being added thereto while preventing for a time of 10 to 30 minutes the formation of an insoluble gel having an SiO 2  /Al 2  O 3  ratio of from 2 to 50:1, adding with stirring an aqueous sodium aluminate which contains 10 to 200 grams/l of Al 2  O 3  and 10 to 250 grams/l of Na 2  O and having a temperature of 10° to 100° C. and allowing the thus obtained synthesis mixture to crystallize at a temperature within between 20° and 175° C. inside at least 15 minutes.

This is a continuation of application Ser. No. 358,268, filed Mar. 15,1982, now abandoned, which is a continuation of Ser. No. 260,764 filedMay 5, 1981, now abandoned, which is a division of Ser. No. 846,014filed Oct. 27, 1977 and now U.S. Pat. No. 4,303,628.

BACKGROUND OF THE INVENTION

The invention is directed to a crystalline zeolite powder of Type Ahaving the composition

    1.0±0.2M.sub.2/n O:Al.sub.2 O.sub.3 :1.85±0.5SiO.sub.2.yH.sub.2 O

wherein M is a metal cation, e.g., sodium, potassium, lithium, calcium,magnesium or barium, n its valence and y has a value up to 6 with 50weight % of the particles not over 4.9μ and a process for the productionof the crystalline zeolite powder by means of a hydrothermalcrystallization of an alkali aluminate silicate mixture, as well as itsuse in washing, rinsing and cleansing agents.

Zeolite molecular sieves and their special properties for ion exchangeand adsorption have been known for a long time. Their synthesis dependson heating an aqueous synthesis mixture with the components a Na₂ OxbAl₂O₃ xcSiO₂ to a temperature between 50° and 300° C. According to thecomposition of the starting mixture, reaction temperature and reactiontime there are obtained different structured compounds of the generalformula

    Na.sub.x Al.sub.x Si.sub.y O.sub.2(x+y).nH.sub.2 O

which are distinguishable by their X-ray spectra. Sodium can be replacedby other mono- and divalent metal cations, e.g., potassium, lithium,cesium, magnesium, barium and strontium.

For use as adsorption agents, catalyst carriers or ion exchangers themolecular sieves are converted into molded articles with a suitablebinder. The production of the molded article means a great industrialexpense with simultaneous reduction of the effect because of the bindercomponent. Also, because of the long diffusion path, the reaction speedis greatly retarded, which, e.g., makes cumbersome the drying of organicliquids. It is, therefore, significant to add molecular sieve powders inmany uses.

The known processes of production (e.g., Milton German Pat. No.1,038,017 and Milton U.S. Pat. No. 2,882,243) have in common thatcrystals are obtained in the molecular sieve synthesis whose averagediameter is above about 2μ, whereby a considerable portion, customarilybetween 3 and 12 weight % have a border grain (limiting particle)diameter above 45μ. This portion is designated grit; it is ascertainedby DIN 53580 (German Industrial Standard 53580) by wet sieving accordingto Mocker. In a typical product for this process, it has beenascertained that about 25 weight % of the particles have a diameterbelow 10μ, 50 weight % have a particle diameter below 13μ (D. W. Breck,Zeolite Molecular Sieves, page 388 (1974)).

The invention is based on the problem of creating a process ofsynthesizing and providing a powdery zeolitic molecular sieve of Type Ahaving a smaller particle size without formation of grit components(particles>45μ), which molecular sieve is especially useful as an ionexchange, e.g., for water softening. Th absence of grit as well as asmaller particle size is indispensable for a number of uses within theinvention, e.g., use of such molecular sieves, e.g., as phosphatereplacements in washing, rinsing and cleansing, processes. Washing,rinsing and cleansing processes, especially in machines, imply indeed alasting suspension of the molecular sieve (as a result of a slighttendency for quiescent setting) in the liquor in order to make possiblea residue free rinsing after completion of the process.

SUMMARY OF THE INVENTION

The purpose of the invention is to produce a crystalline zeolite powderof Type A with the composition

    1.0±0.2M.sub.2/n O:Al.sub.2 O.sub.3 :1.85±0.5SiO.sub.2.yH.sub.2 O

where M is a metal cation, e.g., a Group Ia metal (alkali metal) such assodium, potassium, lithium or cesium or a Group IIa metal (alkalineearth metal) such as magnesium, calcium, strontium or barium, n is itsvalence and y has a value up to 6 with 50 weight % of the particleshaving a maximum particle size of 4.9μ and with a particle spectrum:

    ______________________________________                                        Fraction (μ)                                                                             Portion (weight %)                                              ______________________________________                                         <3           10 to 60                                                         <5           55 to 95                                                        <10           93 to 99                                                        <15            96 to 100                                                      ______________________________________                                    

A further object of the invention is the development of a process forthe production of the crystalline zeolite powder of the invention byhydrothermally crystallizing a SiO₂, Al₂ O₃, Na₂ O and water containingalkali aluminate, water, silicate synthesis mixture with an optionaltempering step wherein in a given case during the crystallization ortempering step instead of stirring shearing forces are employed. Theprocess comprises mixing with stirring (1) an aqueous alkali silicatesolution and (2) an aqueous sodium hydroxide with a NaOH content of 0.1to 500 grams/l and/or (3) aqueous sodium aluminate liquor which contains0.1 to 100 grams/l of Al₂ O₃ and 1 to 200 grams/l of Na₂ O, one ofcomponents (1) and (2) or (3) being present in a container and the otherbeing added thereto while preventing for a time of 10 to 30 minutes theformation of an insoluble gel having an SiO₂ /Al₂ O₃ ratio of from 2 to50:1, adding with stirring an aqueous sodium aluminate which contains 10to 200 grams/l of Al₂ O₃ and 10 to 250 grams/l of Na₂ O and having atemperature of 10° to 100° C. and allowing the thus obtained synthesismixture to crystallize at a temperature within between 20° and 175° C.inside at least 15 minutes.

The alkali silicate solution has 50 to 150 grams of Na₂ O/l and 200 to450 grams of SiO₂ /l.

Shearing can be accomplished, for example, with an energy introductionof 0.4 to 2 KW/m³.

In a preferred form of the invention the aqueous sodium aluminate havinga content of 10 to 200 grams of Al₂ O₃ /l and 10 to 250 grams of Na₂ O/lcan be added stepwise to the reaction mixture, e.g., in two steps,wherein the speed of addition in the second step is 2 to 10 times higherthan in the first step.

Instead of stirrers there can be used in the process of the inventionshearing forces, for which purpose known apparatuses can be employed.These known procedures increase the particle fineness, but are notnecessary for carrying out the process of the invention.

The synthesis mixture arising by the addition of a higher concentratedalkali aluminate liquor can contain the individual components in themolar ratios which are used in the known processes. Such known processesare described in Milton German Pat. No. 1,038,017, Milton U.S. Pat. No.2,882,243 and Weber German Auslegeschrift No. 1,095,795. Thus, the WeberAuslegeschrift shows molar ratios of Na₂ O:Al₂ O₃ of from 2 to 4:1.

In the process of the invention during the crystallization and duringthe in a given case subsequent tempering step shearing forces can act onthe synthesis mixture.

Under the term "shear" as is used in the present case, are allmechanical stresses causing comminution of discrete particles found inthe suspension, which rest predominantly on true shearing action. Theshearing can be carried out discontinuously or continuously.

As the shearing apparatus there is preferred a turbine stirrer, forexample, the EKATO turbine stirrer. However, there can also be usedcrown gear dissolvers, dispersing pumps, centrifugal pumps and otherapparatus for the shearing.

While the crystallization in the present case, for example, can becarried out at 93° C., it has proven advantageous to carry out thetempering in the crystallization mother liquor at a temperature between85° and 105° C., whereby the time of tempering is advantageously between0.2 to 6, most favorably 0.8 to 4.0, particularly one hour.

While crystallization is preferably carried out at 93° C., thistemperature can be varied, e.g., between 90° and 100° C.

The tempering time begins at the point at which the crystallization isfinished. This is recognizable by the development of maximum ionexchange power, the reaching of maximum X-ray line intensity and theproduction of about 22.5% water vapor absorption. In practice afoundation is laid based on empirical values determined by optimizationof a recipe.

A shearing influence up to the end of the crystallization phase can beso intensified that the average particle diameter can be reduced to avery low value. Thereby the value for the limiting particle and itspercentage in the product likewise is reduced. However, shearing carriedout during the tempering step has exclusive influence on the limitingparticle and its portion of all of the particles.

Finally, the invention concerns the use of the zeolitic molecular sievesof Type A, obtainable by the process of the invention, as ionexchangers, e.g., for water softening, particularly as phosphatesubstitutes in washing, rinsing and cleansing agents.

Such washing agents are combinations of surface active washingmaterials, but for the most part also contain other, predominantlyinorganic additives which contribute to the washing result or arenecessary for the process of production and the outer product quality.Depending on the intended use, the composition of the washing agent isvaried. It depends on the type of fiber, dyeing and washing temperature,as well as apart therefrom whether the washing is by hand, e.g., in akettle, in a home washing machine, or in a laundry. Most washing agentsare pourable powders. However, there are also liquid and pasty products(see Ullmann's Enzyklopadie der technischen Chemie, 3rd edition, Vol.18, Urban & Schwarzenberg, Munich, 1967).

The crystalline zeolite powder of Type A produced by the invention hasthe advantage that it is already produced in grit-free form and containssmaller particles. Therefore, when it is used as a phosphate substitutein washing and cleansing agents, it can be easily held in suspension inthe liquor employed, as well as particularly easily rinsed from washingand cleansing machines and their loads.

The use of the alkali aluminum silicates of the invention has theadvantage that the loading of the environment with phosphate will nolonger occur. Eutrophication of the waters, seas and rivers will nolonger result to the presently known extent if the molecular sieves ofthe invention are employed in the washing agent.

Except for replacing of the phosphate by the molecular sieve, thewashing agents are the same as those conventionally employed in the art.Thus, there can be used the conventional surfactants or detergents,e.g., anionic, cationic and nonionic detergents. Thus, as detergentsthere can be used, for example, higher alkyl sulfate detergents,particularly the alkali metal salts of such sulfates, those having 8 to22 carbon atoms in the alkyl residue such as sodium lauryl sulfate,potassium lauryl sulfate, sodium octadecyl sulfate, sodium coconut fattyalcohol sulfate, sodium octanyl sulfate, sodium alkyl (C₁₄ -C₁₈)sulfate, as well as the corresponding long chain aliphatic sulfonates,e.g., sodium octanyl sulfonate, sodium dodecyl sulfonate, sodiumtetradecyl sulfonate, sodium octadecyl sulfonate, potassium dodecylsulfonate, ammonium dodecyl sulfonate, sodium decyl sulfonate, higheralkyl ether sulfates, higher alkyl glyceryl ether sulfonates, higheralkyl phenol polyethylene oxide sulfates, polyoxyethyl ethers of fattyalcohols, polyethylene oxide condensates with higher alkyl phenols suchas isooctyl and nonyl phenol condensed with 3 to 20 moles of ethyleneoxide, sodium o-xylene sulfonate, potassium xylene sulfonate, potassiumtertiary octylbenzene sulfonate, potassium dodecyl toluene sulfonate,sodium p-xylene sulfonate, sodium propyl naphthalene sulfonate, sodiumbutyl naphthalene sulfonate, lauramidodipropyl dimethyl benzyl ammoniumchloride and N-diethylamino oleylamide hydrochloride.

There can also be present conventional additives including bleachingagents, e.g., sodium perborate, water softeners, e.g., borax, as well asother additives including sodium carbonate, sodium sulfate and potassiumcarbonate, as well as polyvinyl alcohol, carboxymethyl cellulose, etc.

The other materials can be omitted if desired.

The compositions can comprise, consist essentially of, or consist of thematerials set forth.

POC is a poly(hydroxycarboxylic) prepared by the Cannizzaro reaction ofa poly(aldehydocarboxylate), see Haschke U.S. Pat. No. 3,923,742.

Unless otherwise indicated all parts and percentages are by weight.

The process of the invention is further explained in connection with thefollowing examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1

There were present in a 2 m³ tank 300 liters of waterglass (d=1.35 kg/l)having a content of 7.4% Na₂ O and 25.6% SiO₂.

There were fed in within 50 minutes under stirring with a three stageMig stirrer to the waterglass at 50° C. 500 liters of an aqueous sodiumaluminate liquor having a temperature of 80° C. and containing Na₂ O=90grams/l and Al₂ O₃ =14 grams/l. Toward the end of the addition turbiditydeveloped.

To the slightly turbid solution there were first added in 25 minutes 100liters of an aqueous sodium aluminate liquor having a temperature of 70°C. and then there were added in 65 minutes a further 850 liters of thesame sodium aluminate liquor at 70° C. The sodium aluminate liquorcontained 148 grams/l of Na₂ O and 103 grams/l of Al₂ O₃. The reactionmixture was warmed to 87° C. and crystallized for two hours. Thecrystalline product was X-ray graphically pure zeolite A having thefollowing particle spectrum:

    ______________________________________                                        Fraction (μ)                                                                             Portion (weight %)                                              ______________________________________                                         <3           40                                                               <5           90                                                              <10           96                                                              <15           100                                                             ______________________________________                                         in which the 50 weight % portion was below 3.2μ.

The particle size determination was carried out by Coulter Countermeasurement.

Example 2

There were present in a 2 m³ tank 560 liters of sodium hydroxide (Na₂O=63 grams/l) at 70° C. There were fed in within 45 minutes understirring with a three stage Mig stirrer 300 liters of waterglass (d=1.35kg/l) having a content of 8.0% Na₂ O and 26.7% SiO₂. The solutionremained clear.

To this solution there were first added in 14 minutes 100 liters ofaqueous sodium aluminate liquor having a temperature of 70° C. and thenthere were added in 100 minutes a further 900 liters of the same sodiumaluminate liquor at 70° C. The sodium aluminate liquor contained 147grams/l Na₂ O and 103 grams/l Al₂ O₃. The reaction mixture was warmed to85° C. and crystallized from three hours. The crystalline product wasX-ray graphically pure zeolite A having the following particle spectrum:

    ______________________________________                                        Fraction (μ)                                                                             Portion (weight %)                                              ______________________________________                                         <3           16                                                               <5           63                                                              <10           99                                                              <15           100                                                             ______________________________________                                    

in which the 50 weight % portion was below 4.4μ.

The particle size determination was carried out by Coulter Countermeasurement.

Example 3

There were present in a 2 m³ tank 550 liters of aqueous sodium aluminateliquor which contained 78 grams/l of Na₂ O and 5 grams/l of Al₂ O₃ at70° C. There were fed in within 44 minutes under stirring with a threestage Mig stirrer 300 liters of waterglass (d=1.35 kg/l) having acontent of 7.4% Na₂ O and 25.7% SiO₂. The solution was clear.

To this solution there were first added in 13 minutes 100 liters ofaqueous sodium aluminate liquor having a temperature of 70° C. and thenthere were added in 65 minutes a further 900 liters of the same sodiumaluminate liquor at 70° C. The sodium aluminate liquor contained 160grams/l Na₂ O and 106 grams/l Al₂ O₃. The reaction mixture was warmed to85° C. and crystallized for three hours. The crystalline product wasX-ray graphically pure zeolite A having the following particle spectrum:

    ______________________________________                                        Fraction (μ)                                                                             Portion (weight %)                                              ______________________________________                                         <3           22                                                               <5           78                                                              <10           99                                                              <15           100                                                             ______________________________________                                    

in which the 50 weight % portion was below 3.8μ.

The particle size determination was carried out by Coulter Countermeasurement.

Example 4

There were present in a 2 m³ tank 550 liters of aqueous sodium aluminateliquor which contained 76 grams/l of Na₂ O and 4 grams/l of Al₂ O₃ at70° C. There were fed in within 20 minutes under stirring with a threestage Mig stirrer 330 liters of waterglass (d=1.35 kg/l) having acontent of 7.4% Na₂ O and 25.5% SiO₂. To this clear solution there werefirst added with stirring in 18 minutes 100 liters of aqueous sodiumaluminate liquor having a temperature of 85° C. and then there wereadded in 70 minutes a further 900 liters of the same sodium aluminateliquor at 85° C. The sodium aluminate liquor contained 161 grams/l Na₂ Oand 105 grams/l Al₂ O₃. The synthesis mixture obtained was warmed to 85°C. and crystallized for three hours. The crystalline product was X-raygraphically pure zeolite A having the following particle spectrum:

    ______________________________________                                        Fraction (μ)                                                                             Portion (weight %)                                              ______________________________________                                         <3           19                                                               <5           75                                                              <10           98                                                              <15           99                                                              ______________________________________                                    

The particle size determination was carried out by Coulter Countermeasurement.

Example 5 Perborate Containing Washing Agent

Sodium aluminum silicate according to any one of Examples 1 to 3: 45.0weight % (dried for 6 hours at 90° C., water content 16.8 weight %).

Sodium perborate: 20.0 weight %.

Washing agent powder: 35.0 weight %.

The washing agent powder was produced, for example, by hot drying thefollowing compositions:

    ______________________________________                                        ABS (sodium dodecylbenzene sulfonate)                                                                    21.0%                                              Ethoxylated tallow alcohol (1 mole tallow alcohol +                                                      7.5%                                               14 moles ethylene oxide)                                                      Soap (sodium salt of saturated essentially                                                               7.2%                                               C.sub.18 -C.sub.22 fatty acids)                                               Waterglass (Na.sub.2 O 3.3 SiO.sub.2)                                                                    9.0%                                               Magnesium sulfate          4.5%                                               Carboxymethyl cellulose    2.0%                                               Optical brightener         0.6%                                               Soluble complex (e.g., sodium citrate, or                                                                9.0%                                               nitrilotriacetic acid (NTA), or ethylene                                      diamine tetraacetic acid (EDTA), or                                           sodium triphosphate, or POC, etc.)                                            Sodium sulfate             35.0%                                              Water                      Balance                                            ______________________________________                                    

The washing agent was produced by mixing the three constituents inpowder form.

Example 6 Perborate Free Washing Agent

Ethoxylated C₁₁ -C₁₅ oxoalcohol (1 mole oxoalcohol+3 moles ethyleneoxide): 2.0 weight % *.

Ethoxylated C₁₁ -C₁₅ oxoalcohol (1 mole oxoalcohol+13 moles ethyleneoxide): 5.0 weight % **.

Sodium aluminum silicate prepared according to any one of Examples 1 to3 (dried for 6 hours at 90° C., water content 16.8 weight %): 40.0weight %.

Soda (sodium carbonate): 15.0 weight %.

Sodium citrate: 5.0 weight %.

Waterglass (Na₂ O 3.3SiO₂): 4.0 weight %.

Carboxymethyl cellulose: 1.5 weight %.

Optical brightener: 0.2 weight %.

Sodium sulfate: 23.0 weight %.

Water: Balance

The washing agent was produced by spraying the ethoxylation product(nonionic surfactant) on the powder particles consisting of theremaining constituents.

What is claimed is:
 1. A process of preparing a crystalline zeolitepower of Type A with the composition

    1.0±0.2Na.sub.2 O:Al.sub.2 O.sub.3 :1.85±0.5SiO.sub.2.yH.sub.2 O

where y has a value up to 6 with 50 weight % of the particles not over4.9μ and with a particle spectrum:

    ______________________________________                                        Fraction (μ)                                                                            Proportion (weight %)                                            ______________________________________                                         <3          40                                                                <5          90                                                               <10          96                                                               <15          100                                                              ______________________________________                                    

comprising hydrothermally crystallizing a SiO₂, Al₂ O₃, Na₂ O and watercontaining alkali aluminate, water, alkali silicate synthesis mixture,said process including the steps of having initially present in a tankat 50° C. 300 liters of waterglass containing 7.4% Na₂ O and 25.6% SiO₂,feeding in 500 liters of aqueous sodium aluminate containing 90 grams/lof Na₂ O and 14 grams/l of Al₂ O and having a temperature of 80° C. andadding further aqueous sodium aluminate to this mixture in two stepswith 100 liters being added in 25 minutes at 70° C. and then a further850 liters of the same aqueous sodium aluminate solution being added in65 minutes at 70° C., the added aqueous sodium aluminate containing 148grams/l of Na₂ O and 103 grams/l of Al₂ O₃, then warming the reactionmixture then to 87° C. and crystallizing for 2 hours.
 2. A process ofpreparing a crystalline zeolite powder of Type A with the composition

    1.0±0.2Na.sub.2 O:Al.sub.2 O.sub.3 :1.85±0.5SiO.sub.2.yH.sub.2 O

where y has a value up to 6 with 50 weight % of the particles not over4.9μ and with a particle spectrum:

    ______________________________________                                        Fraction (μ)                                                                            Proportion (weight %)                                            ______________________________________                                         <3          16                                                                <5          63                                                               <10          99                                                               <15          100                                                              ______________________________________                                    

comprising hydrothermally crystallizing a SiO₂, Al₂ O₃, Na₂ O and watercontaining alkali aluminate, water, alkali silicate synthesis mixture,said process including the steps of having initially present in a tankat 70° C., 560 liters of sodium hydroxide containing 63 grams of Na₂ O/land feeding in 300 liters of waterglass containing 8.0% Na₂ O and 26.7%SiO₂, adding aqueous sodium aluminate to this mixture in two steps with100 liters being added in 14 minutes at 70° C. and then a further 900liters of the same aqueous sodium aluminate solution being added in 100minutes at 70° C., the added aqueous sodium aluminate containing 147grams/l of Na₂ O and 103 grams/l of Al₂ O₃ and allowing the reactionmixture to crystallize at a temperature between 20° and 175° C. for atleast 15 minutes.
 3. A process of preparing a crystalline zeolite powderof Type A with the composition

    1.0±0.2Na.sub.2 O:Al.sub.2 O.sub.3 :1.85±0.5SiO.sub.2.yH.sub.2 O

where y has a value up to 6 with 50 weight % of the particles not over4.9μ and with a particle spectrum:

    ______________________________________                                        Fraction (μ)                                                                            Proportion (weight %)                                            ______________________________________                                         <3          22                                                                <5          78                                                               <10          99                                                               <15          100                                                              ______________________________________                                    

comprising hydrothermally crystallizing a SiO₂, Al₂ O₃, Na₂ O and watercontaining alkali aluminate, water, alkali silicate synthesis mixture,said process including the steps of having initially present in a tankat 70° C. 550 liters of aqueous sodium aluminate containing 78 grams/lof Na₂ O and 5 grams/l of Al₂ O₃, feeding in 300 liters of waterglasscontaining 7.4% Na₂ O and 25.7% SiO₂, and adding further aqueous sodiumaluminate to this mixture in two steps with 100 liters being added in 13minutes at 70° C. and then a further 900 liters of the same aqueoussodium aluminate solution being added in 65 minutes at 70° C., the addedaqueous sodium aluminate containing 160 grams/l of Na₂ O and 106 grams/lof Al₂ O₃ and then allowing the reaction mixture to crystallize at atemperature between 20° and 175° C. for at least 15 minutes.
 4. Aprocess of preparing a crystalline zeolite powder of Type A with thecomposition

    1.0±0.2Na.sub.2 O:Al.sub.2 O.sub.3 :1.85±0.5SiO.sub.2.yH.sub.2 O

where y has a value up to 6 with 50 weight % of the particles not over4.9μ and with a particle spectrum:

    ______________________________________                                        Fraction (μ)                                                                            Proportion (weight %)                                            ______________________________________                                         <3          19                                                                <5          75                                                               <10          98                                                               <15          99                                                               ______________________________________                                    

comprising hydrothermally crystallizing a SiO₂, Al₂ O₃, Na₂ O and watercontaining alkali aluminate, water, alkali silicate synthesis mixture,said process including the steps of having initially present in the tankat 70° C. 550 liters of aqueous sodium aluminate containing 76 grams/lof Na₂ O and 4 grams/l of Al₂ O₃, feeding in 330 liters of waterglasscontaining 7.4% Na₂ O and 25.5% SiO₂, and adding further aqueous sodiumaluminate to this mixture in two steps with 100 liters being added in 18minutes at 85° C. and then a further 900 liters of the same aqueoussodium aluminate solution being added in 70 minutes at 85° C., the addedaqueous sodium aluminate containing 161 grams/l of Na₂ O and 105 grams/lof Al₂ O₃, then allowing the reaction mixture to crystallize at atemperature between 20° and 175° C. for at least 15 minutes.
 5. Aprocess according to claim 2 wherein the crystallization is carried outat 85° to 100° C.
 6. A process according to claim 3 wherein thecrystallization is carried out at 85° C. to 100° C.
 7. A processaccording to claim 4 wherein the crystallization is carried out at 85°to 100° C.